Semiconductor integrated circuits (“ICs”) are packaged in a variety of package styles. Relatively small ICs have been wire-bonded to a frame and encapsulated in molding compound to form a dual in-line (“DIP”) style of packaged ICs. Unfortunately, this approach is not suitable for all ICs, such as ICs that generate a lot of heat. The molding compound does not have sufficiently high thermal conduction to work well with ICs that require good heat dissipation. Metal-ceramic (“ceramic”) packages provide superior heat conduction, but are complex, using various metal-ceramic interfaces, and are relatively expensive.
Other IC packaging has been developed that provides good thermal performance by thermally coupling a molded metal lid to the backside of the IC. The IC (“chip”) is flipped over (“flip-chip”) and electrically connected to the substrate, which is typically a ball-grid array (“BGA”)-type package substrate. BGAs use solder bumps on the frontside of the IC, rather than bond wires, to electrically couple the IC to the package substrate. The BGA package substrate often has another set of solder bumps on the bottom of the package substrate that connect to an array of contacts on a printed circuit assembly. The BGA package substrate includes conductive traces that couple the relatively fine-pitch BGA of the IC to an array of contacts on the printed circuit assembly, which has a relatively coarse pitch.
A pedestal molded into the metal lid is thermally coupled to the backside of the IC with thermal grease. The metal lid also includes a channel around the pedestal that provides space for chip capacitors, which are thicker than the IC and are often soldered to the substrate around the perimeter of the IC. A flat perimeter region of the molded metal lid is attached to the perimeter of the package substrate with adhesive, such as epoxy.
Unfortunately, the molded metal lid is relatively heavy, being more than 60% (12.5 g) of the total package weight (20 g) in a package for a 1-inch square IC. The molding process uses nickel-plated copper typically about 0.094 inches thick to form the lids.
The perimeter areas of the package substrate that the molded metal lid is attached to are quite narrow (about 2 mm to about 3 mm), and provide relatively little surface area for the adhesive contact. The molded metal lids occasionally come off during shipping of the packaged IC, assembly of the packaged IC into an electronic product, or during shipping of the electronic product.
It is desirable to provide a more reliable lid for use with IC packages, namely a lid that is less likely to come off the package substrate due to mechanical shock or vibration.